hiii
i found circuit that use pnp transistor and Comparator to charge battery..every thing work fine but i have one problem

what will happens if i put the battery polarity reversed??

 

You can put an Led and a resistor in parallel with the battery such that the Led is forward biased when the battery is put in backwards so that the light will come on. Size the resistor to set the LED current.

 

nice idea noweare

 

BTDT. If you want to get fancy, You can use a dual color LED, red and green.
I have done this.
The limitation is the 4 volts. You can't run blue or white with a voltage that low.

 

thanks friend..i will try

 

@hertz.12 Do you realize that the circuit you showed will try to change your battery to 5.0 volts? You might also want to add something to limit the current to protect your battery and the transistor.

What is the circuitry to the right of the section you posted?

 

@hertz.12 Do you realize that the circuit you showed will try to change your battery to 5.0 volts? You might also want to add something to limit the current to protect your battery and the transistor.

What is the circuitry to the right of the section you posted?

hi..Comparator and diodes..transistor work as current limitting

 

It looks like 8.6 ma of base current, more or less depending on the actual emitter voltage and temperature, and there is no visible mechanism for limiting the current other than the gain of the transistor. Unless I am misreading the chart that would limit the current to at least 6 amps.



Even if you want 6 amps, depending upon the gain of a transistor to limit current is not a reliable method. I suggest adding a resistor in series with the emitter as a minimum.